Device for powder metering for chemical production processes under clean-room conditions, use thereof and metered addition method

ABSTRACT

Device for metering powder, in particular in clean-rooms, which includes a vessel containing powder and a sealing head with a septum for the vessel, wherein the sealing head is connectable powder-tight with the vessel and the septum powder-tight with the sealing head and the device further includes a vessel holder, which serves to hold the sealing head of the vessel, and the vessel with its opening points downwards, so that the powder can flow out of the vessel, wherein a gap is provided between the sealing head and a holding bowl of the vessel holder, in which a gas flow between the holding bowl and the sealing head can be created. The invention also relates to a use of the device and a metered addition method.

BACKGROUND OF THE INVENTION

The present invention relates to a device for powder metering forchemical production processes under clean-room conditions, the use ofthe device for powder metering and methods for the production ofchemical products using this device.

In chemical production processes such as for example coating orelectroplating, pickling, degreasing, etching, in precipitations, etc.,mixtures of a great variety of substances are used. The concentrationsof the substances concerned must be maintained in a narrow productionwindow in order to ensure always the same production quality. Since notall substances are consumed equally, the concentration of the individualsubstances must be determined and each replenished after deviation fromthe required value. In very many processes, the later metering isperformed in liquid form.

The advantage of liquids is the ease of metering by means of pumps.These are very easy to control and, depending on the volume which isneeded per unit time, easy to scale. Since the substances to be meteredin must be present in dissolved, liquid form, either water or anothersolvent is added to the process as a main constituent. Over a prolongedperiod, this can lead to non-optimal behaviour of the process. Also, thetransport weight of the solution is many times higher than that of thepure dissolved substance which is needed. This leads to increased costsand greater environmental pollution.

In many cases, therefore, solids such as powders or granules are used toreplenish the process. In this way, unnecessary loading of the processwith other substances (water, solvents) and the transport weight can bemarkedly reduced. Also, the storage life of a powder is as a ruleconsiderably longer than that of a liquid concentrate. The aforesaiddisadvantages of metering in liquid form can justify the highertechnical effort of using powder in a method. However, in the latermetering of powder, dust evolution, the danger of contaminating theenvironment during the transfer of the powder from a container into theprocess and also endangerment of the health of persons can arise.

Usually the metering of powders is effected with screw conveyors andconveyor belts of any size. A disadvantage with these transport devicesis that these have a large number of moving parts, which leads tomaterial wear of the transport device. There is also the danger of thiswear and the lubricants used contaminating the powder to be introduced.For many applications, the impurities are so slight that this isrelevant neither for the production process nor for the environment.

On the other hand, in applications such as the pharmaceutical orsemiconductor industry, in which impurities in the smallest quantitiesmust be avoided, this is nonetheless a method uncertainty not to beignored.

A device for the metering of powder with a container with a sealing headand a vessel holder is known from US 2009/0078194 A1.

In the pharmaceutical industry as in the semiconductor industry,production is under clean-room conditions, and dust evolution of anykind under clean-room conditions is a major problem. In clean-roomsaccording to ISO1 to ISO4 (according to ISO 14644-1) no particles ≥5 μmmay be generated or present.

Also, ever more substances are being identified as harmful to health andclassified accordingly. Unfortunately, there is not a harmlessreplacement substance for all these substances. Thus it is veryimportant to protect the staff from health hazards. If substances ofconcern are used in powder form in a production process, the emergenceof powder must be avoided in every case, as can be seen from thefollowing example of the metering of crystalline boric acid into nickelplating electrolytes:

An essential component of the nickel baths is boric acid inconcentrations of up to 45 g/l. In June 2010, boric acid was included bythe ECHA on the candidate list for SVHC (substances of very highconcern). After the GHS order 1272/2008/EG and the REACH modification VO790/2009/EG came into force, boric acid was designated as reprotoxic.According to the GHS order, mixtures which contain boric acid in aconcentration of >5.5% are also to be designated as reprotoxic.Unfortunately, no replacement substances for these applications have yetbeen found. Nickel plating is a widespread surface finishing process andis used in many different industries, such as the automobile and circuitboard industries. Since the solubility of boric acid in water at 20° C.of 47 g/l is very close to the specified concentration of the process,boric acid cannot be replenished as a solution—at least not if thespecified concentration is greater than 25 g/l. For processes with ahigh boric acid concentration, the state of the art is that the additiontakes place manually with crystalline boric acid. The personnel isthereby exposed to a constant hazard. Here a solids metering processwould be the means of choice in order to protect the personnel againstthe hazards.

The same nickel electrolytes are also used in the semi-conductorindustry, where the protection both of the personnel and of theclean-rooms is imperative.

A further example of the advantages of powder metering relates to wafercoating with tin or a tin alloy in the semiconductor industry:

Tin and tin alloy plating on wafers has grown greatly in the last tenyears. Essentially, two tin processes are used on a large scale: theplating of pure tin and of tin alloys. Among the tin alloys, the alloySnAg (tin and silver) is most commonly used, where other alloycomponents such as for example bismuth or copper can also be added tothe tin. In all applications, both with pure tin and also with tinalloys, 1 g to 6 g of tin is typically deposited per wafer. It is notpossible to operate the SnAg process with soluble tin anodes, because ofthe uncontrolled/uncontrollable plating of silver (immersion because ofthe different electrochemical properties of the two metals),consequently inert anodes are as a rule used. A typical production plant(plater) has a throughput of 150 to 400 wafers per day, depending on thenumber of plating chambers available and the plating times. This meansthat per day and plater between 450 g and 2400 g of tin are plated.Replenishing solutions with a concentration of 200 g/l to 400 g/l ofSn²⁺ dissolved in MSA (methanesulphonic acid) are availablecommercially. Thus, per day and tank, 2 to 12 l of metal concentratesmust be added. As a result, after a certain time the tank wouldoverflow. In order to avoid this, a volume of electrolyte correspondingto the volume to be added is aspirated from the tank and as a rule sentto waste. In the best case, this “waste electrolyte” is processed. Forlogistical reasons or as a result of a lack of infrastructure, recyclingof tin is mostly costly and thus not economical.

For most applications in wafer coating, so-called low α tin isexclusively used. The emission rate of a particles is typically lessthan 0.001 cph/cm². Since low α tin in the production process is veryexpensive and the production of the liquid concentrates drives the pricestill higher, it is desirable for cost reasons to avoid waste. Thiswould also be desirable from the environmental viewpoint.

The reaction equations (neglecting the alloying metal) are as follows:Anode: 6H₂O→O₂+4H₃O⁺+4e ⁻Cathode: 2Sn²⁺+4CH₃SO₃ ⁻+4e ⁻→2Sn+4CH₃SO₃ ⁻

At the inert anode, water is cleaved (electrolyzed) and in the processfree acid (H₃O⁺) is formed. As a result, the free acid contentcontinually increases. At the cathode, the tin ions are reduced toelemental Sn. The state of the art is metered addition of the reducedtin as Sn²⁺ methanesulphonate in MSA methanesulphonic acid.

The following disadvantageous effects thereby result:

The tank volume increasing owing to the metered addition must be kept inbalance by the discharge of tin bath liquid (volume to bedischarged=volume to be added).

The MSA content (free acid) increases continually, as a result of whichthe operating point of the electrolyte shifts continually. The behaviourof the organic bath additives is influenced by the changing acidcontent. This has the effect that the plating properties of the processcontinually change. Depending on the process and the structures to beplated, the lifetime of the electrolyte is limited. Typically this limitlies at an MSA concentration of ca. 250 g/l. Depending on throughput,this occurs after a few weeks and the whole tank of ca. 150 l must bedischarged and discarded.

Both of these disadvantageous effects could be avoided if tin monoxideSnO powder could be used for metering the reduced tin according to thefollowing reaction equation:Anode: 6H₂O→O₂+4H₃O⁺+4e ⁻Cathode: 2Sn²⁺+4CH₃SO₃ ⁻+4e ⁻→2Sn+4CH₃SO₃ ⁻Tin Addition:2SnO+4CH₃SO₃ ⁻+4H₃O⁺→2Sn²⁺+4CH₃SO₃ ⁻+6H₂O

The same also applies for the addition of copper(II) oxide CuO.

With this method, both the rise in the free acid and also the increasein the tank volume would be prevented, whereby two positive effectsarise: no electrolyte would have to be discharged in order to avoid anoverflow of the tank, and the content of free acid would remainconstant, as a result of which the lifetime of the electrolyte would besignificantly prolonged.

However, for such a method it would also be necessary to be able to addfurther tin oxide powder or copper(II) oxide powder under clean-roomconditions.

SUMMARY OF THE INVENTION

The present invention is thus based on the problem of providing a devicewhich makes it possible to meter powder in clean-rooms into liquidproduction processes without even the smallest quantities emerging intothe production rooms or personnel being able to come into contact withit.

This problem is solved by the features of Claims 1 and 12.

The device according to the invention for metering powder, in particularinto clean-rooms, comprises a vessel containing powder and a sealinghead with a septum for the vessel, wherein the sealing head isconnectable powder-tight with the vessel and the septum powder-tightwith the sealing head, and a vessel holder which serves to hold thesealing head of the vessel. The vessel points downwards with itsopening, so that the powder can flow downwards from the vessel under theaction of gravity and no additional mechanical means for transport suchas screw conveyors or the like, which can result in wear, are necessary.According to the invention, a gap is provided between the sealing headand the holding bowl of the vessel holder, in which a gas flow betweenthe holding bowl and the sealing head can be created.

Powder residues can be removed from the septum and sealing head by thegas flow.

It is essential that the discharge of the powder and the elimination ofpowder residues on the septum and on the sealing head take placeexclusively on the basis of gravity and on the basis of gas flow, inparticular air flows, and movable mechanical parts are thereby avoided.

In a preferred variant, it is provided that the cross-section of the gapbetween holding bowl and sealing head decreases in the direction of theseptum, so that the flow rate increases in the direction of the septumand owing to the nozzle effect powder residues are at least almostquantitatively removed from the septum and the sealing head.

Preferably, the gap between holding bowl and sealing head is shaped suchthat the flow rate at the septum is maximal and/or the flow is directedagainst the septum, in order completely to remove powder particles fromthe septum and the sealing head. It is especially preferable that theflow rate at the septum is both maximal and is directed against theseptum, i.e. that the angle between the flow rate and the surface of theseptum is preferably between 0 and 45°.

In order to provide a powder-tight seal between the septum and theseptum adapter, the sealing head has a septum adapter and a septum capwith an opening, wherein the septum cap serves to press the septumagainst the septum adapter. In the region of the opening of the septumcap, the septum is accessible and can then in this region be pierced bythe cannula.

A further essential feature of the device according to the invention isthat this is secured against unintended unscrewing of the powder vesselor unscrewing of the sealing head, for if the connections between thepowder vessel and the sealing head or the connections within the sealinghead were detachable, then powder would be able to penetrate outwards.In order to obtain connections which are non-detachable, or notunscrewable with normal forces, complementary locking or snap-onelements are formed on the sealing head and the vessel and/orcomplementary locking or snap-on elements are formed on the septumadapter and the septum cap, which after screwing or pushing of thesealing head onto the vessel or of the septum cap onto the septumadapter together enter into a connection no longer unscrewable withnormal forces and thus not detachable.

The complete emptying of the powder from the powder vessel is preferablyachieved through the vessel inside in the region down to the vesselthread and/or the septum adapter inside being shaped as a funnel and/orthe device having at least one vibrator on the vessel and/or on theseptum adapter.

In the context of the present invention, “powder” is understood to meanany flowable solid, irrespective of the particular particle diameter.

In the vessel holder, the cannula for piercing the septum is provided.In order to fluidize the powder and thus to prevent blockage of thecannula, a gas is fed into the cannula to fluidize the downward flowingpowder, with the gas preferably being fed into the cannula via a sidepipe and via openings in the cannula wall. Thereby a pressureequalization is simultaneously obtained. The side introduction of thegas is advantageous since the cross-section in the inside of the cannulais not diminished. Alternatively, the gas can also be introduced via anadditional pipe in the inside of the cannula.

In general, the air flow is created by suction of the ambient airthrough a suction pipe, whereby the air is sucked in between the sealinghead and holding bowl and is passed via a central hole in the holdingbowl along the cannula to the connector of the suction pipe. It is alsopossible, but less preferable, to blow compressed air into the gap.

In a further preferred variant, the holding bowl of the vessel holder ispressed upwards against a stop on a guide pipe of the vessel holder bymeans of a spring element and the holding bowl is thus pressed againstthe sealing head, so that a defined, reproducible gap is provided forthe air flow. For this, the holding bowl should also be designed suchthat the sealing head is introducible centred into the holding bowl.Notches and/or spacers should be provided on the vessel holder and/orthe sealing head to form the gap.

Preferably, the device according to the invention is further equippedwith a metering system which also dispenses with movable mechanicalparts and is based only on the filling of a defined volume caused bygravity, in such a manner that a volume separable by valves is filledinto a hose and can be emptied.

In order to avoid clumping of the powder, the sealing head connected tothe metering system is preferably heatable.

In a further variant, the sealing head is connected to a mixing vesselwhich has an inlet channel whereby the process liquid is preferablypassed tangentially into the inlet channel and the inlet channelpreferably has an overflow weir in order to prevent powder deposits onthe walls of the mixing vessel.

Also a subject of the present invention is a metering device whichcomprises a vessel containing powder and a sealing head with a septumfor the vessel, wherein the vessel points downwards with its opening, sothat the powder can flow out of the vessel, and the device furthercomprises a vessel holder which serves to hold the sealing head of thevessel, wherein the vessel holder has a cannula for piercing the septumand a gas for fluidizing the downward-flowing powder is fed into thecannula, and furthermore a metering system is provided, which is basedon the filling of a separable volume into a connecting hose, with thebulk density of the powder in the connecting hose being essentially keptconstant through a flow of the gas changing with time during thefluidization. Through the bulk density of the powder flowing into themetering system being kept essentially constant owing to the flow of thegas changing with time, it is quite possible to achieve the metering ofthe powder in clean-rooms via the volume and thus without movable parts,balances, etc.

In a preferred variant, the gas volume of the fluidization is between0.3 and 3.0 times, preferably between 0.5 and 2.0 times the separablevolume in the connecting hose. Also, for a constant bulk density it isadvantageous if the flow of the gas is greatest at the end of thefluidization.

The invention also relates to a vessel containing powder, in particularboric acid, tin(II) oxide or copper(II) oxide, which container has asealing head with a septum, with the sealing head being connectedpowder-tight to the vessel and the septum to the sealing head. Such avessel serves for use for the metering of powder in the device describedabove.

The device according to the invention is particularly suitable for themetering of powders in clean-rooms or for the metering of powdersharmful to health, in particular for the metering of boric acid, tin(II)oxide or Cu(II) oxide.

The present invention also relates to a method for the production ofchemical products, in particular wafers or circuit boards, underclean-room conditions, in particular by coating, electroplating,pickling, degreasing etching, precipitations or chemical reactions,wherein the metered addition of the powders is effected with the deviceaccording to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and further advantageous embodiments and furtherdevelopments thereof are described and explained in more detail on thebasis of the examples shown in the drawings. The features to be learnedfrom the description and the drawings can be used according to theinvention individually per se or as several in any combination.

FIG. 1: a diagrammatic view of the powder metering device according tothe invention, which is shown connected to a mixing vessel,

FIG. 2: a side view of the vessel of the powder metering device of FIG.1 with sealing head and vibrator,

FIG. 3(a): a section view through the vessel with sealing head from FIG.2,

FIG. 3(b): an enlarged view of the circled portion of FIG. 3(a),

FIG. 3(c): an enlarged view of a portion of FIG. 3(b) that shows ingreater detail how locking or snap-on elements provided on the septumadapter lock/snap into complementary locking or snap-on elementsprovided on the vessel above the vessel thread,

FIG. 3(d): an enlarged view of a portion of FIG. 3(b) that shows ingreater detail how the septum cap locks onto the septum adapter,

FIG. 3(e): an enlarged view of a portion of FIG. 3(b) that shows ingreater detail the connection of the septum to the septum cap,

FIG. 4: an exploded view of the vessel with sealing head from FIG. 3(a),

FIG. 5(a): a section view through the vessel with sealing head and thevessel holder from FIG. 1,

FIG. 5(b): an enlarged view of a portion of FIG. 5(a) that shows the airflow in the gap,

FIG. 5(c): an enlarged simplified view of the circled portion of FIG.5(b) that shows the shape of the gap in the region of the septum,

FIG. 6(a): the a top view of the holding bowl of FIG. 5(a) that showsthe notches and the spacers,

FIG. 6(b): a section view of the holding bowl of FIG. 6(a) along lineA-A,

FIG. 7(a): a side view of the vessel with the sealing head, beforeactuation of the knee lever mechanism,

FIG. 7(b): a side view of the vessel with the sealing head afteractuation of the knee lever mechanism,

FIG. 8: a section of the vessel holder with the cannula and the sealinghead in section corresponding to FIG. 5(a), but with pierced septum,

FIG. 9: an example of an airflow-time diagram of a fluidization,

FIG. 10: a section view through the metering system shown in FIG. 1,

FIG. 11(a): a side view of the mixing vessel of FIG. 1,

FIG. 11(b): a section view of the mixing vessel of FIG. 11(a) takenalong line A-A,

FIG. 12: an enlarged section view of the upper region of the mixingvessel from FIG. 11(b),

FIG. 13: a top view of a connector of the mixing vessel,

FIG. 14: a side view of a mixing vessel with two powder meteringdevices,

FIG. 15: a schematic design of a plant for an electroplating processwith liquid metered addition according to the prior art and

FIG. 16: a schematic design of a plant for an electroplating processwith a powder metering device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the design of the powder metering device 23 according to theinvention, which is connected via a metering hose 33 to a mixing vessel42 is shown diagrammatically. The powder 59 is located in a vessel 56,the opening 56 a whereof is directed downwards. The vessel 56 has aspecial sealing head 57 and is fitted into the vessel holder 58, seealso FIGS. 2, 3(a)-3(e), 4, and 5(a)-5(c). The vessel holder 58 enablesthe dust-free outflow of the powder 59 into the metering hose 33, fromthere into the connecting head 34 and from there into the mixing vessel42, where the powder 59 dissolves in the process liquid.

The structure of the sealing head 57 is shown in FIGS. 2, 3(a)-3(e), and4. As shown in FIG. 2 and FIGS. 3(a)-3(e), the sealing head 57 isscrewed onto the vessel thread 111 of the vessel 56 instead of a normaltwist closure. As a result, normal commercial vessels 56 can be used. Asshown in the exploded drawing FIG. 4 the sealing head 57 consists, ofthe following parts: a sealing element 112, namely an O-ring, a septumadapter 113, a septum 115 and a septum cap 114.

The O-ring 112 seals between vessel thread 111 or the lower end of thevessel 56 and the septum adapter 113. As a result, the powder 59 isprevented from emerging at the connection site. The O-ring 112 isselected such that it effects a secure seal between the vessel thread111 and the septum adapter 113 with all tolerances which arise from theindividual parts in the screwed-together state.

It is important that the septum adapter 113 cannot separateunintentionally from the vessel thread 111, since otherwise powder 59would emerge in an uncontrolled manner. In order to prevent this,locking or snap-on elements 116 are provided on the septum adapter 113,which on complete screwing on of the septum adapter 113 lock/snap intocomplementary locking or snap-on elements 117 provided on the vessel 56above the vessel thread 111.

Above the vessel thread 111, the outer wall of the vessel 56 extendsradially slanting slightly outwards and forms a sliding surface 117 a,so that the septum adapter 113 can easily be screwed or pushed upwardsalong this slanting outer wall 117 a of the vessel 56, whereby it isslightly pressed outwards on its upward-facing side. Above the slope 117a, the outer wall 117 b of the vessel 56 extends radially inwards andforms a barrier surface 117 b running perpendicular to the longitudinalaxis of the vessel 56, behind which a holding space 117 c is formed forthe locking nose 116, also running radially inwards, on the septumadapter 113, which on pushing/screwing upwards locks into the holdingspace 117 c. Through the locking nose 116 of the septum adapter 113being in contact with the radially inward-facing surface 117 b of thevessel, the septum adapter 113 can no longer be unscrewed or pusheddownwards, so that the locking/snap-on connection 116 is not releasableby screwing, see FIGS. 3(b) and 3(c).

Through the design of the sliding surface 117 a, it is possible withlittle force to screw the septum adapter 113 on, but almost impossibleto remove this again after the locking hook 116 of the septum adapter113 is snapped over complementary locking element 117 b and c.

It must also be ensured that no powder 59 can emerge between septumadapter 113 and septum 115. When the septum cap 114 is screwed onto theseptum adapter 113, the septum 115 is pushed through the septum cap 114into the septum adapter 113 and prevents the emergence of powder 59.

Here also, it is necessary to prevent the septum cap 114 from beingdetachable unintentionally from the septum adapter 113. This is solvedanalogously to the previously described locking or snap-on connection116, 117 b and 117 c, between the septum adapter 113 and the vessel 56,in such a manner that the septum adapter 113 also has a sliding surface119 a directed slightly outwards radially (see FIGS. 3(b) and 3(d)), sothat the upper side of the septum cap 114 when screwed in and pushedupwards is pressed slightly outwards and then after travelling over thesurface 119 b running radially inwards at right angles to thelongitudinal axis spring-locks with the locking hook 118 in the freespace 119 c. Since the barrier surface 119 b runs at right angles to thelongitudinal axis of the septum adapter 113, the locking connection canno longer be released by a screwing-on movement or by pulling downwards.

The vessel 56, the septum adapter 113 and the septum cap 114 can be madeof various metals, coated metals, plastics or glass. It is notabsolutely necessary that all parts be made of the same material.Preferably, chemically stable plastics are used. This ensures that eventhe smallest quantities of these plastics cannot adversely influence theprocess liquid.

As soon as the vessel 56 has been completely emptied of the powder 59,it can be removed from the vessel holder 58 together with the sealinghead 57 and replaced with a full vessel 56′ with sealing head 57.

The sealing head 57 can either be discarded or else recycled in aspecial process.

The septum 115 is made of an elastomer. Depending on the application,various elastomers can be used, such as natural rubber, syntheticrubber, ethylene-propylene rubber EPM, fluoro elastomers FKM and FEPM,perfluoro elastomer Kalrez®, ethylene-vinyl acetate EVA, butyl rubbersand others. Because of their chemical and physical properties, butylrubbers are particularly preferred as material for the septum, sincethey are very resistant to acids and alkaline solutions and are elasticand have a Shore A hardness of 40 to 85 and an elongation at break of700%. The good chemical stability is important since in the unlikelyevent that very small particles were nonetheless to get into the processliquid, this would not be adversely affected. The good elasticity andthe good elongation at break enable reliable piercing of the septum 115in the vessel holder 58, without the powder 59 emerging during thisprocedure, and likewise secure sealing of the septum 115 after theremoval of the vessel 56 from the vessel holder 58 and the withdrawal ofthe cannula 134 associated therewith. It is important that after theremoval of the vessel 56 from the vessel holder 58 the septum 115independently seals again and thus prevents the emergence of powder 59from the vessel 56.

The shape of the septum 115 can be a disc or, as in the section shown inFIGS. 3(a), 3(b), 3(e) and 4, shaped as a plug. The plug shape ispreferred, since this shape yields a secure seal between the septumadapter 113 and the septum 115 during the piercing and withdrawal. Thelarge sealing area of the plug shape ensures a secure seal even on theoccurrence of large forces on the septum 115, as occurs during piercingor withdrawal. The pressing forces which are required by the septum cap114 in the region of the septum 115 can be kept small through the plugshape of the septum 115 and nonetheless ensure a good seal. As a result,the wall thicknesses needed can be kept thin. Thus it is possible toform a transition from the septum cap 114 to the septum 115 beneficialto flow, as shown in FIGS. 3(e) and 5 in the transition region 120.

Internally in the region up to the vessel thread 111, the vessel 56 hasthe shape of a funnel. And the septum adapter 113 inside up to theseptum 115 is also shaped as a funnel. This shaping makes it possible toempty the whole of the powder 59 from the vessel 56. Depending on thepowder type and vessel 56, it can be necessary to vibrate, so that thepowder 59 reliably falls downwards in the direction of the septum 115and the vessel 56 can be completely emptied.

In order to achieve complete emptying of the powder 59 from the vessel56, one or more vibrators 49 can be provided on the vessel 56 and/or oneor more vibrators 50 on the septum adapter 113 (FIGS. 1 and 2). The siteand number of the vibrators 49 and 50 is strongly dependent on thenature of the powder 59 and the shape of the vessel 56.

The vibrator 50 on the septum adapter 113 has been found very effective.This arrangement vibrates sufficiently to completely empty the vessel56, without compacting the powder 59 so strongly that a blockage occurs.In order to configure the effect of the vibration reproducibly evenafter frequent changing of the vessel 56, the septum adapter 113 has onits outer wall a beading 110 (FIG. 2), which ensures that irrespectiveof the exact positioning of the vibrator 50 the vibrations are alwaysintroduced at the same place in the septum adapter 113. As vibrators,for example electromechanical, piezo-electric, pneumatic vibrators oreccentric vibrators can be used.

The vessel 56 with sealing head 57 and septum adapter 113 is insertedinto the vessel holder 58. In order to fill the metering hose 33 withthe powder 59, the cannula 134 in the vessel holder 58 is pierced intothe septum 115, and the powder 59 flows downwards in the cannula 134(see FIGS. 5(a) and 5(b) and FIG. 8). Via a pipe 52, which extends atright angles to the longitudinal direction of the cannula 134, gas ispressured by means of the fluidization pump 25 into the downward-flowingpowder in the cannula 134 in order to fluidize this. For this, the gasis passed through the holes 139 in the outer wall of the cannula 134shown in FIG. 5(a). As a result, the flowability of the powder 59 isensured and the volume of the powder flowing into the metering hose 33replaced by gas. Thus no negative pressure arises in the vessel 56 andno gas has to flow against the flow direction of the powder 59. Thisensures reproducible filling of the metering hose 33. By means of apump, both the volume and also the rate at which the gas is pressuredinto the powder 59 can be very precisely set.

In order to achieve high reproducibility of the powder volume to bemetered, it is necessary that the bulk density of the powder whichreaches the metering system be as constant as possible.

On the one hand, the powder in the region of the cannula has a differentbulk density depending on the fill level of the vessel.

On the other hand, non-reproducible bulk densities in the meteringsystem can also derive from a negative pressure in the vessel, since gasis then sucked from the measurement system into the vessel against theflow direction of the powder. Thus it is necessary to replace the volumeof the powder taken from the vessel with gas, in order to avoidnon-reproducible bulk densities in the metering system.

According to the invention, before the transfer into the meteringsystem, the powder is fluidized by the fluidization pump 25, with whichgas is pressured into the downward-flowing powder, and in such a mannerthat the flow of the gas changes with time during the fluidization. Inthis way, the bulk density in the metering system can be keptessentially constant. The fluidization is performed before the openingof the pinch valve 28.

It is also important that the fluidization occurs only in a limitedregion of the cannula, so that the gas is accumulated very locally,before the powder is transferred into the metering system.

In a first variant, the pump 25 is controlled such that before meteringthe same airflow-time profile is always used for the fluidization, asshown in FIGS. 11(a) and 11(b).

A further improvement of the reproducibility of the bulk densities canbe achieved in a further variant by adapting the airflow-time profile tothe particular fill level of the vessel.

The total gas volume for the fluidization corresponds to about 0.3 to3.0 times and preferably 0.5 to 2.0 times the volume of the meteringsystem (I*di²*π/4).

The variation of the gas flow with time essentially corresponds to thedegree of spreading of the gas cushion in the powder in the region ofthe cannula. It is important that the gas is not accumulated only in thecannula, but also emerges from the cannula into the vessel. It is evenimportant that the major part of the gas reaches the lower part of thevessel. Hence the greatest gas volume is pressured into the powder atthe end of the fluidization.

FIGS. 11(a) and 11(b) show the variation of the gas flow with timeduring a fluidization by means of a pump. Preferably, the flow of thegas firstly increases slowly and reaches maximum flow rate before theend of the fluidization. Depending on the properties of the powder, itis necessary to set a fluidization typical for a powder.

Alternatively, a time-controlled valve can also be used instead of apump. Depending on the properties of the powder 59 to be metered,various gases can be used, where dry and oil-free air, nitrogen andargon can be mentioned as the most usual. Nitrogen and argon are readilyused if the powder for example can oxidize or is hygroscopic.

Via the suction pipe 63, which extends above the fluidization pipe 52,the vessel holder 58 is aspirated permanently or from time to time,depending on the use. The dust filter 26 (FIG. 1) prevents particlesfrom getting into the exhaust air pump 27. This arrangement, which isshown diagrammatically in FIG. 1, can also be replaced by a centralexhaust air system. Then the suction pipe 63 is connected directly tothe central exhaust air system. Likewise, the outlet of the dust filter26 can be connected to an exhaust air system, whereby entry of particlesinto the exhaust system is prevented, since these are retained by thedust filter 26.

FIG. 5(a) shows the longitudinal section through the vessel holder 58with applied, non-inserted sealing head 57. The sealing head 57 isinserted into the holding bowl 131 of the vessel holder 58. The holdingbowl 131 is shaped such that the sealing head 57 is introduced centredinto the holding bowl 131. This is achieved by means of the threenotches 137 on the holding bowl 131, see FIG. 6(a). More than threenotches 137 can also be provided. Also, spacers 138 are provided which,together with the notches 137, provide a defined air gap 200 betweensealing head 57 and holding bowl 131. More spacers 138 can also bepresent. These can also be adjustable, so that the air gap 200 in theregion of the septum 115 can be adjusted to the required flow rate. Flowrates of 2-35 m/s are required depending on the properties of the powder59, and the materials used for the production of holding bowl 131,septum cap 114 and the septum 115 and the surface condition thereof.

In FIG. 5(b), the airflow in the gap 200 is shown as a dashed line. Theairflow is created by the aspiration of the ambient air via the suctionpipe 63. The air is sucked in between holding bowl 131 and sealing head57 and passed via the central hole in the holding bowl 131 along thecannula 134 to the connector of the suction pipe 63 in the holding lowerpart 133.

Through the continuously decreasing cross-section between holding bowl131 and sealing head 57, the flow rate increases continuously and isgreatest in the region of the septum 115. The septum cap 114, whichengages the septum 115 in its edge region partially from below, has inthe direction of the centre of the septum 115 a rounded edge 135, asshown in FIG. 5(b), which is designed to favour the flow. The centralregion of the septum 115 does not lie on the septum cap 114, but isaccessible. The holding bowl 131 on its upward-facing side lyingopposite the central region 120 of the septum 115 has a rounding 136corresponding to the underside of the rounded edge 135 of the septum cap114, so that the airflow is directed upwards in the direction of theseptum 115, as shown in FIG. 7(b). As a result, the best possible flowonto the septum 115 is ensured. This flow onto the septum 115 ensuresthat particles falling out during the piercing of the septum 115 withthe cannula 134 or during the withdrawal of the cannula 134 can bespecifically aspirated. It is thus ensured that no particles remainhanging on the septum 115 or on the sealing head 57. Thus the vessel 56can be removed from the vessel holder 58 without there being a risk thatparticles can escape into the surroundings. Depending on the materialfrom which the individual parts are made and the properties of thepowder 59, it can be necessary to ionize the air drawn in. This preventsthe possibility of the particles not being removable by suction becauseof static charge.

A pressure spring 132 presses the holding bowl 131 upwards to a catch131 a in the guide pipe 130 of the vessel holder 58. The spring 132 ispre-tensioned such that the septum 115 cannot be pierced by the cannula134 because of the weight of the vessel 56 itself. This preventsuncontrolled piercing of the septum 115 by the cannula 134 fromoccurring. Controlled piercing of the septum 115 with as uniform aspossible a movement is necessary in order to prevent the emergence ofpowder 59 during the piercing of the septum 115. In the simplest case, aknee lever 141 can be used, as shown in FIG. 7(a) and FIG. 7(b), inorder to press the vessel 56 downwards, in order to pierce the septum115 with the cannula 134, see FIGS. 5(a) and 5(b) and FIG. 8. If theknee lever 141 is released again, the vessel 56 is pressed against theknee lever 141 by the spring 132, so that a controlled withdrawal of thevessel 56 with the sealing head 57 with the septum 115 from the cannula134 is ensured. Instead of a manual knee lever 141, automatic driveswith or without knee lever 141, such as pneumatic, hydraulic orelectrical systems, can also be used.

The cannula 134 pierces the septum 115 so far that the ground point ofthe cannula 134 comes to rest inside the vessel 56, so that the powdercan flow into the cannula.

In order to prevent the emergence of powder 59 during the piercing andwithdrawal of the cannula 134 from the septum 115, the shape of thepoint and the cut of the cannula 134 is decisive. It has been found thatthe ratio of the thickness of the septum 115 to cannula externaldiameter in the range from 0.4 to 1.0 is ideal. Various cuts on thecannula 134 can be used. The best known are lancet cut, facet cut andothers which are known from medicine. It is important that during thepiercing no hole is punched in the septum 115, but the whole septum 115is only pierced and parts of the septum 115 do not get into the cannula134 or into the powder 59.

With the powder metering device according to the invention, a definedvolume of powder 59 can now as required be metered as follows. If theseptum 115 is pierced with the cannula 134, then the powder 59 flowsthrough the cannula 134 into the metering hose 33. The metering systemis shown in section in FIG. 10 and diagrammatically in FIGS. 11(a) and11(b). If the pinch valve 28 is closed, then the metering hose 33 fillsup to the pinch valve 28. If the pinch valve 28 is open and the pinchvalve 31 shut, then the metering hose 33 fills from the vessel 56 up tothe pinch valve 31. If the pinch valve 28 is closed and the pinch valve31 opened, the powder flows between the pinch valves 28 and 31 throughthe connector head 34 into the mixing vessel 42. The volume of themetered powder 59 is calculated from the distance 1 and the internaldiameter di of the metering hose 33, as shown in FIG. 10. By variationof the distance between the two pinch valves 28 and 31, the volume ofthe powder 59 to be metered can be adjusted. During the emptying of themetering hose 33, gas can be pumped via the hose 53 into the outletnozzle 140 by means of the pump 32. This serves to push the powder 59out of the metering hose 33 in a controlled manner. The outlet nozzle140 is attached directly after the pinch valve 28. Dry air, nitrogen,argon or other suitable gases can be used. Instead of the outlet nozzle140, a vibrator 51 can also be attached on the metering hose 33 in orderto guarantee the complete outflow of the powder 59. Outlet nozzle 140and vibrator 51 can also be used together. Instead of the pump 32, atime-controlled valve with or without choke can also be used.

The metering hose 33 should be of an elastic material with good recoverybehaviour. Suitable hose materials are silicone, neoprene, marprene,fluoro elastomer, PFL-reinforced fluoro elastomers and others. Themetering hose 33 can also be made in rigid pipes and only made with anelastic hose in the region of the pinch valves 28 and 31. Since thetolerances of the internal diameter of elastic hoses are as a rulegreater than those of pipes, the metering volume from position toposition is more reproducible with pipes. With the described structureof a metering hose 33 (with or without pipe) a repetition accuracy ofthe metered-in volume of <1% can be achieved.

The connector head 34 is maintained at a higher temperature than theambient temperature. This prevents blockages being able to occur due tomoisture at the outlet of the connector head 34. The connector head 34can be maintained at a defined temperature by means of a heatingcartridge and a temperature sensor, shown as heating 35 in FIG. 1. Thetemperature control of the connector head 34 can be effected by means ofother media, for example with hot fluids or gases.

With the temperature sensor 39, the process management system 12 can setthe temperature of the connector head 34 such that condensation cannotoccur on the connector head 34. By means of the pump 52, the gas spaceabove the process liquid 24 can be specifically flushed with gas via theconnection 61. Usual gases are dry air, nitrogen and argon through theintroduction of gas, the humidity in the space can be reduced and theblocking of the outlet at the connector head 34 thereby prevented. Alsoby the use of suitable gases, the oxidation of the powder 59 and theprocess liquid 24 can be reduced or prevented. Instead of the pump 52, atime-controlled valve with or without choke can also be used.

With the powder sensor 29, it can be established whether the meteringhose 33 between the pinch valves 28 and 31 is completely filled. Withthe powder sensor 30, it can also be established whether the meteringhose 33 has emptied itself after the opening of the pinch valve 31.Measurement principles suitable for the powder sensors 29 and 30 are forexample capacitive, ultrasonic or infrared measurement.

When the powder 59 leaves the connector head 34, then it falls into themixing vessel or dissolving vessel 42, where the powder 59 mixes withthe process liquid 24 or dissolves. The fill level of the process liquid24 in the mixing vessel 42 is regulated such that this is kept betweenthe fill level sensors 37 and 38. For this, the valves 19, 18, 21 andpump 43 are available to the process management system 12. The processmanagement system 12 regulates the fill level such that it permanentlyfluctuates up and down between the fill level sensors 37 and 38. In thisway, deposits due to powder 59 on the walls of the mixing vessel 42 areprevented. Instead of or in addition to the fill level sensors 37 and38, a continuous fill level measurement can be used in order toguarantee better fill level regulation. In order to guarantee goodmixing and/or dissolution of the powder 59 with the process liquid 24, astirrer 36 is built into the mixing vessel 42. This is controlled by theprocess management system 12. Mechanical stirrers, magnetic stirrers orhydraulic mixers for example the tank mixer PTM-200 from Levitronix, canbe used. In FIG. 11, a cross-section through the mixing vessel 42 with ahydraulic mixer is shown.

Process liquids 24 often have an elevated temperature of up to 90° C. Inorder to ensure that the process liquid 24 does not cool down in themixing vessel 42, the mixing vessel 42 can be made double-walled 40. Ifan exothermic reaction takes place during the dissolution of the powder59, it is necessary to remove the energy produced. This can be effectedby means of a temperature control system 41. The cooling or heatingfluid is pumped by the temperature control system 41 via the pipe 54into the intermediate space and again back into the temperature controlsystem 41 via the pipe 55. The materials for the mixing vessel 42 mustbe chosen according to the use. Fluorinated plastics are used inparticular since these are temperature-resistant and have very goodchemicals resistance.

On the emergence of the powder 59 from the connector head 34, the powdercan deposit on the walls of the mixing vessel 42. In order reliably toprevent the powder depositing on the walls of the mixing vessel 42 abovethe maximum level of the process liquid 24, the inlet into the mixingvessel 42 is equipped with an overflow weir 161. The process liquid 24is passed into the inlet channel 160 via the pipe 20 (shown in FIG. 12).The pipe 20 (FIG. 1) is connected to the connector 162, which passes theprocess liquid 24 tangentially into the inlet channel 160, shown in FIG.13. Through this tangential introduction, an almost uniform pressuredistribution in the inlet channel 160 is achieved. Thus the processliquid 24 flows uniformly through the holes 163 to the overflow weir161. From the overflow weir 161, the process liquid 24 flows downwardsalong the wall on the mixing vessel 42 and permanently washes any powderresidues into the process liquid 24 and thus prevents accumulation ofpowder 59 on the side walls.

As required, the process management system 12 can permanently pass theprocess liquid 24 through the mixing vessel 42, and during this thevalve 18 is closed and the valves 19 and 21 open. Or else, before thepowder metering, valves 19 and 21 are closed and valve 18 opened, thenthe desired volume of powder 59 is fed into the mixing vessel 42 andduring a defined time the powder 59 blends or dissolves. After this,valve 18 is closed and the valves 19 and 21 opened and the pump 43 sucksprocess liquid from the mixing vessel 42 via pipe 60 and maintains thecirculation. If a hydraulic mixer is used, pump 43 and mixer can beintegrated together.

Depending on the process, it can be necessary to purify the processliquid 24 from undesired particles after the dissolution of the powder59. This can take place by means of one or more filters 45 and 47. Itcan also be necessary that one of the filters 45 and 47 is made as anactivated charcoal filter in order to filter out undesired compounds.The pressure sensors 44, 46 and 48 are for monitoring the filters 45 and47 and can detect clogging. Centrifuges can also be used.

For one mixing vessel 42, two powder metering devices 23 can beprovided, which use a common connector head 34, as shown in FIG. 14. Inthis way, the metering process does not have to be interrupted when onevessel 56 becomes empty. The process management system 12 then switchesautomatically from the empty to the full vessel 56. Now the operatingpersonnel have time to replace the empty vessel 56 by a full one,without interrupting the metering process.

In FIG. 15, the prior art is shown diagrammatically with the example ofan electroplating process with liquid metered addition, and in FIG. 16an example of the plant known from the prior art, in which the powdermetering device 23 is built in.

The workpieces are coated with a metal layer in the production machine1, FIGS. 15 and 16. The cathode 5 is electrically connected to theworkpiece in the plating chamber 2. The anode 6 can be of a more inertmaterial such as for example titanium, platinum or stainless steel or ofthe material to be deposited, such as for example copper or nickel. Thequantity of material deposited on the workpiece is determined by thepower source 7 from the quantity of charge Q, which is calculated viathe current I and the time t. The plating chamber 2 is fed by theprocess pump 9 from tank 4 in order to guarantee a constant double layeron the cathode 5. From the tank 4, the process fluid 24 in the tank 4 iscirculated with the circulation pump 8.

After the process pump 9 and the circulation pump 8, particle filterscan be incorporated (not shown). From the circulation pipe 3, a smallvolume of the process liquid 24 is passed to the process managementsystem 12 after the circulation pump 8 via the sampling pipe 11. Theprocess management system 12 determines the concentration of theindividual components of which the process liquid 24 is composed. Theproduction machine 1 and the process management system 12 exchange datavia the communication line 10. These data are needed inter alia tocalculate the metering quantities of individual additional meteringconcentrations 16 by the process management system 12. The additionalmetering unit 14 is controlled by the process management system 12 viathe communication line 13. On the basis of the analysis data and thedata from the production machine 1, the process management system 12continuously calculates the required metering volumes of the individualadditional metering concentrations 16 and monitors the metering process.The individual pumps 15 pump the concentrates via the additionalmetering pipes 17 into the circulation pipe 3.

The connectors of the additional metering pipes 17 must be attached onthe circulation pipe 3 after the offtake of the sampling pipe 11, so asto prevent over-concentrated process liquid 24 reaching the processmanagement system 12, false analytical results being generated and falseadditional metering volumes being calculated.

In FIG. 16, the plant from FIG. 15 is shown, to which the powdermetering device 23 according to the invention is connected together withthe relevant lines and valves. The powder metering device 23 iscontrolled and monitored by the process management system 12. Via thedata line 150, the data necessary for this are exchanged between thesystems, similarly to in the additional metering unit 14 described inFIG. 15. The circulation pipe 3 is divided into circulation pipe 3 a andcirculation pipe 3 b by the bypass valve 18. Via the feed valve 19 andthe feed pipe 20, the process liquid 24 in which the powder 59 isdissolved is passed to the powder metering device 23. Via the returnpipe 22 and the return valve 21, the process liquid 24 with thedissolved powder 59 is fed into the circulation pipe 3 b. If no powdermetering takes place, the bypass valve 18 is closed and the circulationis permanently passed through the powder metering device 23. It isthereby ensured that there are no stagnating process liquids 24 in thewhole system. In case of longer dissolution times of the powder 59, itcan be necessary during the dissolution time to open the bypass valve 18and to close the feed valve 19 and the return valve 21. It is thusensured that the other functions as described in FIG. 15 continue tofunction without restriction. After completion of the dissolution time,the bypass valve 18 is closed and the feed valve 19 and the return valve21 opened. With appropriate design of the powder metering device 23, thereturn valve 21 can also be replaced by a non-return valve.

The invention claimed is:
 1. A device for metering powder, whichcomprises a vessel containing powder and a sealing head with a septumfor the vessel, wherein the sealing head is connectable powder-tightwith the vessel and the septum with the sealing head, and the devicefurther comprises a vessel holder, which serves to hold the sealing headof the vessel, and the vessel with its opening points downwards, so thatthe powder can flow out of the vessel, wherein a gap is present betweenthe sealing head and a holding bowl of the vessel holder, in which a gasflow between the holding bowl and the sealing head can be created. 2.The device according to claim 1, wherein the cross-section of the gapbetween the holding bowl and the sealing head decreases in the directionof the septum, so that the flow rate of the gas increases in thedirection of the septum.
 3. The device according to claim 1, wherein thegap between the holding bowl and the sealing head is shaped such thatthe flow rate is maximal on the septum and the flow is guided againstthe septum in order to remove powder particles from the septum and thesealing head.
 4. The device according to claim 1, wherein the sealinghead has a septum adapter and a septum cap with an opening, wherein theseptum cap serves to press the septum against the septum adapter.
 5. Thedevice according to claim 1, wherein complementary locking or snap-onelements on the sealing head and the vessel and/or complementary lockingor snap-on elements on a septum adapter and a septum cap are formed,which enter into a non-detachable or difficult to detach connection withone another after respectively the sealing head is screwed or pushedonto the vessel and the septum cap onto the septum adapter.
 6. Thedevice according to claim 1, wherein the vessel inside in the regiontowards a vessel thread and/or a septum adapter inside is shaped as afunnel and/or the device contains at least one vibrator on the vesseland/or on the septum adapter.
 7. The device according to claim 1,wherein the vessel holder has a cannula for piercing the septum and agas for fluidizing the downward-flowing powder is fed into the cannula,wherein the gas is fed into the cannula via a side pipe and via openingsin the cannula wall.
 8. The device according to claim 1, wherein airflow is created by suction of the ambient air via a suction pipe, theair is sucked in between the sealing head and the holding bowl and ispassed via a central hole in the holding bowl along the cannula to aconnector of the suction pipe.
 9. The device according to claim 1,wherein the holding bowl of the vessel holder is pressed upwards againsta catch on a guide pipe of the vessel holder by means of a springelement and/or the holding bowl is formed such that the sealing head canbe introduced centred into the holding bowl and/or notches and/orspacers are provided on the vessel holder and/or the sealing head toform the gap.
 10. The device according to claim 1, wherein the devicefurther has a metering system which is based on the filling of a volumein a connecting hose separable by valves.
 11. The device according toclaim 10, wherein an attachment head which is heatable is attached tothe metering system.
 12. The device according to claim 11, wherein theattachment head is connected to a mixing vessel which has an inletchannel wherein the process liquid is introduced preferably tangentiallyinto the inlet channel and the inlet channel preferably has an overflowweir in order to prevent powder deposits on the walls of the mixingvessel.
 13. A method for powder metering, the method comprisingproviding the device according to claim 1, and using the device to metera powder in a clean-room or to meter a powder harmful to health.
 14. Themethod according to claim 13 wherein the powder is made of a materialselected from the group consisting of boric acid, tin(II) oxide andcopper(II) oxide.
 15. A vessel containing powder, which container has asealing head with a septum, wherein the sealing head is connectedpowder-tight to the vessel and the septum powder-tight to the sealinghead, which vessel is used in a device for metering powder according toclaim
 1. 16. The vessel containing powder according to claim 15, whereinthe powder is made of a material selected from the group consisting ofboric acid, tin(II) oxide and copper(II) oxide.
 17. A method forproducing chemical products under clean-room conditions, the methodcomprising metering powder with the device according to claim 1 andproducing chemical products with the metered powder.
 18. The methodaccording to claim 17 wherein the chemical products are wafers, circuitboards, substrates or multi-chip modules.
 19. The method according toclaim 17, wherein the production under clean-room conditions is effectedby coating, electroplating, pickling, degreasing, etching,precipitations or chemical reactions.